Generally, ink is required not only to achieve excellent color reproduction, but also to enable the formation of images which excel in water fastness and light fastness. Further, in printing of inkjet recording which forms images by ejecting ink droplets onto recording media, the ink is required to exhibit more limited characteristics than those demanded for ink employed for common writing utensils such as a fountain pen or a ball-point pen. For example, the ink for inkjet recording is required to exhibit appropriate viscosity, surface tension and stability, and not to cause nozzle clogging.
Printers for inkjet recording commonly employ a yellow ink, a magenta ink, and a cyan ink, as well as arbitrarily a black ink, and create various kinds of colors via superposition of these colored inks to form color images. Each of the colored inks, employed in the printer of the inkjet recording system as described above, is required to excel in individual color reproduction and in addition, is required to excel in reproduction of red, green, and blue which are created by superposition of inks.
In general, many characteristics required for the ink for inkjet recording, as described above, are achieved via an aqueous ink composition which incorporates water-soluble dyes, and water and/or water-soluble organic solvents. Further, various characteristics of color images, such as color tone, water fastness, or light fastness depend on properties of employed water-soluble dyes, and consequently, utilization of various water-soluble dyes has been tried.
For example, Patent Documents 1-9 disclose applications of phthalocyanine compounds as a cyan colorant to form a cyan ink.
However, any of these phthalocyanine compounds provide neither high dispersion stability nor high light fastness, and a cyan ink has not been realized, which provides these characteristics.
Patent Documents
    (Patent Document 1) U.S. Pat. No. 5,296,023    (Patent Document 2) U.S. Pat. No. 5,704,969    (Patent Document 3) U.S. Pat. No. 4,632,703    (Patent Document 4) U.S. Pat. No. 5,123,960    (Patent Document 5) Japanese Patent Application Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 61-2772    (Patent Document 6) JP-A No. 62-149758    (Patent Document 7) JP-A No. 62-190273    (Patent Document 8) JP-A No. 2003-128949    (Patent Document 9) JP-A No. 3-200,883